A gas operated automatic or semi-automatic firearm of the standard M16 or AR15 type is a popular weapon which has been used for many years by both the military and civilian population. A very essential part of this firearm is called the bolt carrier assembly and typically the bolt carrier assembly includes a bolt carrier, a bolt mounted in the carrier for axial sliding movement and rotation, a firing pin slidably mounted within the bolt and bolt carrier for restricted reciprocating axial movement, and a cam pin for producing relative rotation between the bolt and the bolt carrier. The bolt carrier is generally cylindrical in shape and is provided with a circular bore throughout its length. The bolt carrier also is provided with an opening on its top and bottom sides to allow the hammer to extend into the interior of the bolt carrier and strike the firing pin. There are also openings to mount a gas key, an opening which serves as a gas receiving port, and an opening to receive the cam pin. About the exterior of the bolt carrier are a series of usually four (4) lands and usually accompanying grooves which extend from the forward end of the bolt carrier (as it is mounted in the firearm) rearwardly for a distance of about one-half the length of the bolt carrier. A land can be defined as a raised portion on the exterior of the bolt carrier which contacts the interior surface of the upper receiver of the firearm. Such lands are generally equally spaced from one another about the exterior of the bolt carrier and are generally parallel to each other. The exterior surface of the lands make contact with the interior surface of the upper receiver of the firearm and serve to align the bolt carrier within the receiver. A firearm of the M16 or AR15 type has the capability of firing a large number rounds of ammunition in a very rapid manner. However, the accuracy of the firearm leaves something to be desired and any improvement in the firearm which tends to increase its accuracy and the smoothness and consistency of operation is very desirable.